The present invention relates generally to the radiation detection field and, more particularly, to a radiation detection method and apparatus capable of distinguishing between neutron and gamma radiations.
It is often desirable or necessary to simultaneously monitor neutron and gamma radiation. For example, spent reactor fuel emits neutrons while other radioactive waste does not. Consequently, the movement of spent reactor fuel within an underwater fuel basin may be monitored by sensing or detecting the presence of neutrons. A problem arises, however, in that it is difficult to detect neutrons in the presence of an associated large flux of gamma rays as, for example, emitted by the spent fuel and other radioactive wastes in the fuel basin.
In an effort to overcome this problem, several detection mechanisms have been proposed involving scintillation. Gamma rays and neutrons that reach a scintillation detector produce flashes of light as they lose their energy through nuclear reactions in the scintillator. The light flashes due to the neutrons may be distinguished from those due to the gamma rays by the shape of the output.
Examples of such scintillation detectors are found in U.S. Pat. Nos. 3,566,118 to Peters, 3,786,253 to Haftner et al and 3,988,586 to Stewart et al. While such scintillator devices are capable of providing reasonably accurate neutron and gamma ray readings, they are not without their disadvantages.
Each of the devices requires the use of photomultiplier tubes for counting the pulses or flashes of light created by the neutrons or gamma rays impinging upon the scintillator. Disadvantageously, these photomultiplier tubes are quite expensive. Further, as the flux of gamma rays increases, the efficiency and ability of the photomultiplier tubes in distinguishing between the pulses or flashes created by the neutrons and gamma rays in the scintillator is greatly reduced.
Thus, a need is identified for an improved method and apparatus for distinguishing between neutrons and gamma rays. More particularly, a need is identified for a method and apparatus that is less expensive while providing improved efficiency and distinguishing ability.